1. Field of the Invention
The present invention relates to a finishing machine of concrete surface comprising rotatable trowels for leveling the surface of deposited concrete, and more specifically to a finishing machine of concrete surface with which the efficiency of automated finishing work on the surface is improved.
2. Background Art
In the past, the finishing work of the surface of concrete consisted of the following steps: placing concrete; laying mortar on it thereafter; and leveling the surface of the mortar. However, this mortar finishing method has drawbacks that the mortar layer scales off and cracks appear therein. In addition, the plastering work requires a great deal of skill and labor and the environment has become worse with this finishing method. In order to avoid these drawbacks, finishing according to the so-called "Monolithic method" has been utilized in which the surface of concrete is directly finished before it hardens. As a result, when level finishing work is carried out by plasterers after concrete is placed, there have arised problems that high working speed is required in summer because of fast setting of concrete and that labor management till midnight may sometimes be necessary in winter. So as to solve these new problems, the working conditions have been improved step by step as follows: plastering work using a trowel was mechanized; working speed was increased by using a mechanically rotatable single trowel; labor of plasterers was reduced and posture of the plasterers during the work became more comfortable; a plurality of rotatable trowels were used; and finally a finishing machine of concrete surface was realized in which control devices are integrated in the body thereof as well as the rotatable trowels. Owing to these improvements, mechanization of surface finishing work of concrete not yet hardened has been realized, which has lead to the reduction of labor of plasterers and to automatization of the finishing work. However, it is not very long since the robotization of such a finishing machine of concrete surface began, and, in general, the working capacity of the machine has not yet fully developed.
At present, the finishing machine of concrete surface is automated to the point that electromotive rotatable trowels are integrated in a single body so that they are able to move automatically and work on the concrete surface by revolution both on its axis and around the central axis of the machine. In the course of step-by-step development so far, several problems have been encountered. The performance of the machine must always be adapted to the succeeding working step by taking into account the nature of concrete.
The first problem relates to the weight of finishing machine. So as to lighten the machine and limit the pressure exerted by the trowels to the concrete surface, aluminum members which are not strong enough and high in cost are used as frames and the number and nature of equipments mounted to the machine are also restricted. Finishing machines of concrete surface so far developed are electromotive in which a plurality of rotatable trowels are each equipped with an electric motor, which leads to a too heavy machine. The second problem originates from he necessity of supplying electric power to the electric motors when the finishing machine is traveling. Because the body of the finishing machine always trails cables for power supply, the cables risk not only to damage the concrete surface under finishing treatment but also to get twisted around the rotatable trowels and in the worse they may be cut by the latter. In order to avoid these problems, various attempts have been made. However, each attempt has generated another new restriction. The third problem relates to the improvement of precision of the finished surface and the realization of high working speed. For this purpose, the speed of revolution of rotatable blades around their axis is chosen to be between 70 and 80 r.p.m. and accordingly the traveling speed of the finishing machine is determined to be 6 m/min. However, the speed of revolution of the rotatable trowels around their axis is so high that the concrete surface tends to be disturbed in the early stage of finishing as in that by a float. Therefore, the lifetime of the trowels is shortened. In addition, the total floor area treated by the finishing machine, 3,500 m.sup.2, is not sufficient. The fourth problem relates to the noise made by engines when the means for driving each of the trowels is changed from electric motors to engines. If the finishing work after the placement of concrete is prolonged till midnight, noise made by the engines disturbs the silence in the neighborhood. These problems described just above still remain to be solved.
The present invention was accomplished through intensive research in view of avoiding the above-mentioned drawbacks of the actual electric finishing machine of concrete surface to provide an excellent finishing machine of concrete surface with a gasoline engine which is mounted to the machine as a result of reexamination of the construction of the rotatable trowels from the point of view of their working capacities.
Another object of the present invention is to provide a finishing machine of concrete surface which is not only capable of finishing the surface of deposited concrete with high precision depending on its surface state but also adaptable to the driving means mentioned above and to the nature of concrete by equipping the support members which support rotatable trowels of the prior art with a means for angle adjustment so as to change the angle of the surface of revolution of the rotatable trowels with the concrete surface through the support members and accordingly to change the speed of revolution of the rotatable trowels around the axis of the finishing machine.
Another object of the present invention is to provide a finishing machine of concrete surface which is capable of executing the finishing work depending on the degree of hardening of concrete by equipping the finishing machine with a means for adjusting contact pressure of the traveling means of the finishing machine and that of the rotatable trowels with the concrete surface which changes the ratio between the contact pressure with the concrete surface of the rotatable trowels and that of the traveling means.
A further object of the present invention is to provide, based on the finding that the number of rotatable blades is preferable to be 5 without restricting it to be 3, a finishing machine of concrete surface in which the lifetime of the trowels is prolonged, the noise is reduced, and a reduction in cost is realized by increasing the supporting area of the rotatable blades on the concrete surface to increase the total supporting force, which makes it possible not to use lightweight frames, and accordingly by equipping the finishing machine with a small engine with smaller rotation frequency.
Yet another object of the present invention is to simplify the structure of transmission shafts by arranging them equally around the central axis of the finishing machine toward the radial direction while making the central axis pass through a gearbox so as to leave freedom to the position of the engine in distributing the output power from the engine toward each rotatable trowel through the gearbox.
Yet further but not the last object of the present invention is to provide a finishing machine of concrete surface in which the noise level is lowered by using belts instead of transmission shafts to transmit the output power from the engine toward each rotatable trowel.